Remove "no depdencies" statement from README

As is apparent from the current go.mod file, this library definitely depends on various other libraries.
This in turn makes it depend on Go 1.13 (currently).

README.md

@@ -11,7 +11,7 @@ The goal is to make simple to write simple XMPP clients and components:
 - For writing simple chatbot to control a service or a thing,
 - For writing XMPP servers components.
 
-The library is designed to have minimal dependencies. For now, the library does not depend on any other library.
+The library is designed to have minimal dependencies. Currently it requires at least Go 1.13.
 
 ## Configuration and connection